The present report is the first in a projected series of investigations on biogenic amine-synthesizing and-degrading enzymes in trophoblast. The work is being undertaken to gain information relating to two questions. First, do the placental enzymes which degrade biogenic amines and related compounds provide an important biochemical barrier which protects the fetus against undesirable stimulation by physiological and pharmacological compounds in the maternal circulation? Secondly, do critical changes in biogenic amine metabolism in the placenta precede or accompany parturition, and might they be involved in the actual mechanism underlying the initiation of parturition ? Catechol-O-methyltransferase (COMT, E.C.2.1.1.6) is an enzyme which inactivates certain catecholamines and O-methylates 2-hydroxyoestradiol-17\g=b\ (Ball, Knuppen, Haupt & Breuer, 1971); it has been purified 66-fold from human placenta (Gugler, Knuppen & Breuer, 1970). We report COMT levels in rat placenta at various stages of gestation, in human placenta at term, and in choriocarcinoma grown in culture.
Summary. The (Edlow, Köhler & Robinson, 1972). Tissues were homogenized in 9 vols of 0-167 M-potassium chloride for 3 min in an Omni-Mixer (Ivan Sorvall, Inc., Newtown, Connecticut), and the enzyme activity in the homogenates was assayed.The assay for MAO was a modification of the method of Wurtman & Axelrod (1964). In a total volume of 500 pi, the incubation mixture contained 250 mM-potassium phosphate buffer, pH 7-4; 0-5 mM-[2-1+C]tryptamine bisuccinate, 0-0325 pCi; and 100 pi enzyme preparation. At the end of incubation at 37°C for 20 min, a 0-2 ml volume of 2 n-HCI was added to stop the reaction. Toluene (1 ml) was then added for extraction of the product. After centrifugation, 0-5 ml toluene extract was added to 10 ml scintillation fluid and the radioactivity was determined. The enzyme activities were expressed in units (nmol product/hour) per g wet wt, per mg protein, per placenta, or per rat, as indicated after correction for 83 % recovery. Protein was determined by the method of Lowry, Rosebrough, Farr
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